If you’ve ever cooked a chicken breast and had it turn out tough and chewy, it might not have been your fault. Some chickens are affected by a condition called “woody breast,” which is the result of hardened muscle fibers. The exact cause is unknown, but it’s linked to chickens that have been bred to get as big as possible as quickly as possible. Most producers check for it by feeling for knots in the breasts, and either grind or discard those that have them, but it’s not always possible to detect before cooking. Woody breast is believed to affect 5% to 10% of the chicken breasts on the market, and though not a health threat to humans, it’s certainly not pleasant to eat. To lessen the chance of getting a woody breast, buy your chicken from smaller farms.